Ultra-wideband systems such as are used in radar, RF sensing, and communications systems typically rely on application of a short impulse signal to an antenna, which then radiates an ultra wideband signal. The characteristics of the radiated signal are largely based on the impulse response of the antenna, as the applied impulse is typically in the tens of picoseconds to nanosecond range. The propagated RF signal then typically has a fixed center frequency and fixed bandwidth, both of which can be in the multi-gigahertz range.
While such a system may be well suited for radar or other RF monitoring purposes, data communications applications require some method of modulating the signal or encoding information on the propagated RF signal. On-off keying (OOK), pulse position modulation, and other modulation techniques have been implemented to encode information into transmitted ultra wideband pulses, which can then be used to transmit information at a rate that is dependent on the ultra wideband system's pulse repetition frequency.
Technology such as avalanche transistors and zener diodes is commonly used to create such pulses, but even impulse excitations of several thousand watts typically result in less than one watt of peak microwave-band output power. Further, because the semiconductor devices tend to heat at such power levels, the pulse repetition rate is then limited to approximately 10 kHz or less. Much of the energy produced at frequencies lower than microwave is not propagated but is instead dissipated as heat, which can have a negative impact on circuit reliability.
Ultra wideband technology nevertheless remains desirable for some applications because it is difficult to detect or intercept, and such signals are difficult to jam. The impulse nature of ultra wideband transmission and the low power of the radiated signal virtually require exact synchronization between a receiver and transmitter, so that the receiver can accumulate enough pulses to provide a high probability of a detected signal. Ultra wideband radar or communications equipment also only minimally degrade the noise floor of other nearby RF equipment, making integration of ultra wideband systems into existing assemblies of various communication or radar equipment relatively nonintrusive.
But, these ultra wideband systems typically employ periodic or psuedorandomly timed pulses that are themselves uniform in configuration, making detection of pulses in radar applications straightforward. While such pulses work well for radar applications, they do not lend themselves well to other communication applications as they have not been adapted to carry information.
What is desired is an ultra wideband pulse generation system that can carry information, and that is low in cost and in power consumption.